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Implementation of CONCISE (COmpressed 'N" Composable Integer SEt) bit map compression algorithm by Alessandro Colantonio with some enhanced features - http://ricerca.mat.uniroma3.it/users/colanton/concise.html

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/* 
 * (c) 2010 Alessandro Colantonio
 * 
 * 
 *  
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */ 


package it.uniroma3.mat.extendedset.wrappers.matrix;

/**
 * A class for representing a single transaction-item relationship. This class
 * is mainly used in {@link PairSet} to iterate over the cells of a
 * binary matrix.
 * 
 * @author Alessandro Colantonio
 * @version $Id: Pair.java 140 2011-02-07 21:30:29Z cocciasik $
 * 
 * @param 
 *            transaction type
 * @param 
 *            item type
 * @see PairSet
 */
public class Pair implements java.io.Serializable {
	/** generated ID */
	private static final long serialVersionUID = 328985131584539749L;

	/** the transaction */
	public final T transaction;
	
	/** the item */
	public final I item;

	/**
	 * Creates a new transaction-item pair
	 * 
	 * @param transaction
	 * @param item
	 */
	public Pair(T transaction, I item) {
		this.transaction = transaction;
		this.item = item;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public int hashCode() {
		// 524287 * i = (i << 19) - i, where 524287 is prime.
		// This hash function avoids transactions and items to overlap,
		// since "item" can often stay in 32 - 19 = 13 bits. Therefore, it is
		// better than multiplying by 31.
		final int hi = item.hashCode();
		final int ht = transaction.hashCode();
		return (hi << 19) - hi + ht;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public boolean equals(Object obj) {
		if (obj == null)
			return false;
		if (this == obj)
			return true;
		if (!(obj instanceof Pair))
			return false;
		@SuppressWarnings("unchecked")
		Pair other = (Pair) obj;
		return transaction.equals(other.transaction) && item.equals(other.item);
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public String toString() {
		return "(" + transaction + ", " + item + ")";
	}
}